Response behavior of ZrO2 under swift heavy ion irradiation with and without external pressure

In this study, we demonstrate that the combination of relativistic heavy ions with pressure can influence the phase behavior of ZrO2 in ways none of those two extreme conditions alone could. The response behavior of ZrO2 towards ion irradiation under different pressure conditions is investigated. ZrO2 exposed to energetic particles is known to undergo a crystalline-to-crystalline phase transition from the monoclinic to the tetragonal phase. In agreement with earlier findings, this structural change requires also for heaviest ions, such as Au, Pb, and U, a multiple ion impact. If the irradiation is performed under high pressure, the monoclinic-to-tetragonal transformation occurs at a fluence that is more than one order of magnitude lower suggesting a single impact process. Raman measurements at ambient conditions and X-ray diffraction analysis of the samples irradiated under pressure revealed that the monoclinic-to-tetragonal transformation under pressure is not a direct process but involves a transition into the cubic high-temperature structure, before the tetragonal structure becomes stable under decompression. At even higher pressures, the additional ion irradiation forces ZrO2 to transform to the higher orthorhombic-II phase that is far away from its stability field.